1. Field of the Invention
The present invention relates to a high-frequency circuit and a reception device, and particularly to a high-frequency circuit having a filtering function and a reception device.
2. Description of the Background Art
In general, a filter circuit allowing passage of a prescribed frequency component such as a frequency component from approximately 10 GHz to 12 GHz in a received high-frequency signal is employed in a satellite broadcast reception device. Conventionally, a microstrip type half-wave filter has widely been used as such a filter circuit.
For example, Japanese Utility Model Laying-Open No. 02-134706 (Patent Document 1) discloses the following filter as such a microstrip type filter. Specifically, in a microstrip coupled-line type band-pass filter including a plurality of coupled-lines each consisting of a pair of microstrip lines in parallel, a ground conductor in a portion occupied by the coupled-lines in an input portion and an output portion is removed.
In addition, Japanese Patent Laying-Open No, 2001-320202 (Patent Document 2) discloses the following filter. Specifically, the filter includes a dielectric substrate, a microstrip conductor metal film formed on a surface of the dielectric substrate, a back-surface metal film formed over the entire back surface of the dielectric substrate, and a plurality of internal spaces formed at prescribed intervals along a direction of extension of the microstrip conductor metal film at a position directly under the microstrip conductor metal film in the inside of the dielectric substrate.
Moreover, Japanese Patent Laying-Open No. 07-283621 (Patent Document 3) discloses the following directional coupler. Specifically, in improving directional characteristics of an asymmetrical directional coupler in which a back surface of a printed board serves as a ground conductor and a coupler line shaped like a pair of tapered openings is provided on an upper surface in a microstrip line, a pattern cut-out obtained by cutting away the ground conductor in a triangular shape is provided in the ground conductor directly under the back surface of the coupler line, as means for mitigating difference in an effective dielectric constant between even-mode propagation and odd-mode propagation.
In a half-wave filter, a plurality of resonators having an electrical length comparable to approximately ½ of a wavelength corresponding to each frequency of a signal in a frequency band that should pass through the filter are required. Accordingly, an area occupied by the filter is disadvantageously large.
A configuration for forming a trap by connecting an open stub having an electrical length comparable to ¼ of the wavelength corresponding to a frequency of a signal to be attenuated to a transmission line is possible as a configuration for attenuating a signal having a specific frequency. In such a trap as well, a space for connecting an open stub should be ensured, and layout of a circuit pattern is restricted.
Patent Documents 1 to 3, however, are silent about a configuration for solving these problems.